Applications of Isotopes

1. Carbon-14 Dating

Most of the carbon on earth exists as the non-radioactive isotope ¹²C. However, a very small percentage exists as ¹⁴C. We take ¹⁴C into our bodies by eating and breathing. However, after death, we stop incorporating ¹⁴C into our bodies and the ¹⁴C begins to decay. It breaks down into ¹⁴N atoms and electrons, decreasing the amount of ¹⁴C in the body.

As time goes on, the concentration of ¹⁴C just keeps decreasing and decreasing. We know that the half-life of ¹⁴C is 5760 years. That is the amount of time that it takes for half of the atoms to change into nitrogen atoms. If we measure the concentration of ¹⁴C in a sample, we can work backwards to determine about how old the sample is. This technique is useful for finding the age of things that lived between about 2000 and 50,000 years ago.

One famous use of ¹⁴C dating is the dating of Eqyptian mummies. The picture below is a mummy from the Niagara Museum in Georgia.

Another famous case that involved ¹⁴C dating was the Shroud of Turin, a cloth that some claim to be the burial cloth of Christ. It is presently displayed in the Vatican.

2. Medical Use of Isotopes

There are many isotopes that are used in medicine. For example, ⁶⁰Co is used to produce a beam of radiation that is used in killing cancer cells. Along with cancer therapy (oncology), a number of isotopes are used for medical imaging. These radioactive isotopes are injected into the body, and then imaging devices follow the path of these isotopes through the body. Some of the tracer isotopes include:

• ²⁴Na - used for diagnosing circulatory problems
• ⁹⁹Tc - used for diagnosing brain, heart and organ problems
• ¹³¹I - used for diagnosing thyroid problems

The images below were taken using positron emission tomography (PET). This technique scans for positrons emitted by several isotopes, including ¹¹C and ¹⁰F. This particular image shows brain activity of a patient with Parkinson's disease.




3. Nuclear Power

The two isotopes most commonly used for nuclear power are ²³⁵U and ²³⁹Pu. While a comprehensive treatment of nuclear power is beyond the scope of this course, a few points about how nuclear power works are worth noting here:

• The uranium fuel rods undergo nuclear reactions, usually underwater. The water slows the neutrons down so that the reactions can occur.
• The heat from the nuclear reactions heats up the water.
• This heat is transferred to a second container of water, which turns into steam and turns the turbine.

That second container of water produces the great clouds of steam that you see when you drive past a nuclear reaction. That second container is completely separated from the compartment that contains the radiation, so it is in no way dangerous.


Of course the main dilemna in nuclear power is what to do with the used fuel rods. They remain radioactive for many lifetimes and have to be stored in a completely dry, stable environment. Also, it should be noted that the spent nuclear fuel can be recycled and used for nuclear weapons: situations which have certainly been in the news recently.

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